Add polyfill for Luxon example code to work in IE11

docs/index.html

@@ -3,6 +3,7 @@
 		<meta charset="utf-8">
 		<meta name="viewport" content="width=device-width, initial-scale=1">
 		<title>Financial | Chart.js</title>
+		<script src="https://cdn.polyfill.io/v2/polyfill.js?features=default,String.prototype.repeat,Array.prototype.find,Array.prototype.findIndex,Math.trunc,Math.sign"></script>
 		<script src="https://cdn.jsdelivr.net/npm/luxon@1.15.0"></script>
 		<script src="https://cdn.jsdelivr.net/npm/chart.js@2.8.0"></script>
 		<script src="https://cdn.jsdelivr.net/npm/chartjs-adapter-luxon@0.1.1"></script>